M-Theory (The theory formerly known as Strings)

Superunification underwent a major paradigm shift in 1984 when eleven-dimensional supergravity was knocked off its pedestal by ten-dimensional superstrings. This last year has witnessed a new shift of equal proportions: perturbative ten-dimensional superstrings have in their turn been superseded by a new non-perturbative theory called M-theory, which describes supermembranes and superfivebranes, which subsumes all five consistent string theories and whose low energy limit is, ironically, eleven-dimensional supergravity. In particular, six-dimensional string/string duality follows from membrane/fivebrane duality by compactifying M-theory on S1/Z2 ×K3 (heterotic/heterotic duality) or S1 ×K3 (Type IIA/heterotic duality) or S1/Z2 × T 4 (heterotic/Type IIA duality) or S1 × T 4 (Type IIA/Type IIA duality).

Multi-Membrane Solutions of D = 11 Supergravity

We find exact solutions to the field equations of eleven-dimensional supergravity corresponding to stable multi-membrane configurations. Their holonomy group is given by the SO (8) subgroup of an enlarged tangent space group SO ( l, 2 ) × SO (16), and hence one half of the spacetime supersymmetries are broken. The solutions saturate a Bogomol'nyi bound between the mass per unit area and the Page charge, which also guarantees their stability.